Solvent-based inks comprising coated magnetic nanoparticles

ABSTRACT

Solvent-based ink compositions which can be used for ink jet printing in a variety of applications. In particular, the present embodiments are directed to magnetic inks having desirable ink properties. The ink of the present embodiments comprise magnetic nanoparticles that are coated with various materials to prevent the exposure of the nanoparticles to oxygen, and provides robust prints.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly owned and co-pending, U.S. patentapplication Ser. No. 13/050,268 entitled “Curable Inks ComprisingInorganic Oxide-Coated Magnetic Nanoparticles” to Iftime et al.; U.S.patent application Ser. No. 13/050,152 entitled “Solvent-Based InksComprising Coated Magnetic Nanoparticles” to Iftime et al.; U.S. patentapplication Ser. No. 13/050,403 entitled “Magnetic Curable Inks” toIftime et al.; U.S. patent application Ser. No. 13/049,936 entitled“Phase Change Magnetic Ink Comprising Carbon Coated MagneticNanoparticles And Process For Preparing Same,” to Iftime et al.; U.S.patent application Ser. No. 13/049,937 entitled “Solvent Based MagneticInk Comprising Carbon Coated Magnetic Nanoparticles And Process ForPreparing Same” to Iftime et al.; U.S. patent application Ser. No.13/049,942 entitled “Phase Change Magnetic Ink Comprising CoatedMagnetic Nanoparticles And Process For Preparing Same” to Iftime et al.U.S. patent application Ser. No. 13/049,945 entitled “Phase ChangeMagnetic Ink Comprising Inorganic Oxide Coated Magnetic NanoparticlesAnd Process For Preparing Same” to Iftime et al.; U.S. patentapplication Ser. No. 13/050,341 entitled “Curable Inks ComprisingSurfactant-Coated Magnetic Nanoparticles” to Iftime et al.; U.S. patentapplication Ser. No. 13/050,383 entitled “Curable inks ComprisingPolymer-Coated Magnetic Nanoparticles” to Iftime et al.; U.S. patentapplication Ser. No. 13/049,950entitled “Phase Change Magnetic InkComprising Surfactant Coated Magnetic Nanoparticles and Process ForPreparing the Same” to Iftime et al.; and U.S. patent application Ser.No. 13/049,954 entitled “Phase Change Magnetic Ink Comprising PolymerCoated Magnetic Nanoparticles and Process for Preparing the Same” toIftime at al., all filed electronically on the same day as the presentapplication, the entire disclosures of which are incorporated herein byreference in its entirety.

BACKGROUND

Non-digital inks and printing elements suitable for Magnetic InkCharacter Recognition (MICR) printing are generally known. The two mostcommonly known technologies are ribbon-based thermal printing systemsand offset technology. For example, U.S. Pat. No. 4,463,034 disclosesheat sensitive magnetic transfer element for printing MICR, comprising aheat resistant foundation and a heat sensitive imaging layer. Theimaging layer is made of ferromagnetic substance dispersed in a wax andis transferred on a receiving paper in the form of magnetic image by athermal printer which uses a ribbon. U.S. Pat. No. 5,866,637 disclosesformulations and ribbons which employ wax, binder resin and organicmolecule based magnets which are to be employed for use with a thermalprinter which employs a ribbon. MICR ink suitable for offset printingusing a numbering box are typically thick, highly concentrated pastesconsisting for example in about over 60% magnetic metal oxides dispersedin a base containing soy-based varnishes. Such inks are, for example,commercially available at Heath Custom Press (Auburn, Wash.). Digitalwater-based ink-jet inks composition for MICR applications using a metaloxide based ferromagnetic particles of a particle size of less than 500microns are disclosed in U.S. Pat. No. 6,767,396. Water-based inks arecommercially available from Diversified Nano Corporation (San Diego,Calif.).

The present embodiments relate to solvent-based ink compositions. Theseink compositions can be used for ink jet printing in a variety ofapplications. In addition to providing desirable ink qualities, thepresent embodiments are directed to magnetic inks for use in specificapplications. The ink of the present embodiments comprise magneticnanoparticles that are coated with various materials to prevent theexposure of the nanoparticles to oxygen. The present embodiments arealso directed to a solvent-based magnetic ink that provides robustprints.

The present embodiments are directed to solvent-based magnetic inkswhich comprise an organic solvent, an optional dispersant, an optionalsynergist, an optional antioxidant, an optional viscosity controllingagent, an optional colorant, and coated magnetic nanoparticlescomprising a magnetic core and a coated shell disposed thereover. Thesemagnetic inks are required for specific applications such as MagneticInk Character Recognition (MICR) for automated check processing andsecurity printing for document authentication. One of the challenges informulating such a solvent-based ink, however, is that many of thesemetal nanoparticles are pyrophoric and extremely sensitive to air andwater. For example, iron nanoparticles can burst into flame instantlyupon exposure to air. As such, uncoated magnetic metal nanoparticles area serious fire hazard. As such, large scale production of thesolvent-based inks comprising such particles is difficult because airand water need to be completely removed when handling the particles. Inaddition, the ink preparation process is particularly challenging withmagnetic pigments because inorganic magnetic particles are incompatiblewith organic base components. Lastly, a problem associated with the useof the magnetic solid inks is the solid ink vehicle is designed fornormal office use and not the highly abrasive environment of multiplepasses through a magnetic reader. As a result, a magnetic solid inkprint may wear off quickly during machine-reading process, either forMICR or for document authentication procedures.

Thus, there is a need for a magnetic ink which can be printed withpiezoelectric print-heads and which can be made both safely and providesrobust prints compatible with solvent-based compositions.

Thus, while the disclosed solid ink formulation provides some advantagesover the prior formulations, there is still a need to achieve aformulation that not only provides the desirable properties of asolvent-based ink but is also more easily produced and derived fromcomponents that do not require special handling conditions.

SUMMARY

According to embodiments illustrated herein, there are providedsolvent-based ink compositions which produce robust prints and which canbe used for ink jet printing in a variety of applications. The ink ofthe present embodiments comprise magnetic nanoparticles that are coatedwith various materials, such as for example, polymers, surfactants andinorganic oxides, to prevent the exposure of the nanoparticles tooxygen. The present embodiments are also directed to a solvent-basedmagnetic ink that provides robust prints.

In particular, the present embodiments provide a magnetic inkcomprising: an organic solvent carrier; an optional dispersant; anoptional synergist; an optional antioxidant; an optional viscositycontrolling agent; an optional colorant; an optional binder; and coatedmagnetic nanoparticles, wherein the coated magnetic nanoparticles arecomprised of a magnetic metal core and a protective coating disposed onthe magnetic metal core, the coated magnetic nanoparticles beingdispersed in the solvent carrier and further wherein the protectivecoating is selected from the group consisting of polymeric materials,inorganic oxides, surfactants and mixtures thereof.

In further embodiments, there is provided a magnetic ink comprising: asolvent carrier; an optional dispersant; an optional synergist; anoptional antioxidant; an optional viscosity controlling agent; anoptional colorant; an optional binder; and coated magnetic nanoparticlescomprising a magnetic metal core and a protective coating disposed onthe magnetic metal core, the coated magnetic nanoparticles beingdispersed in the solvent carrier and wherein the protective coatingcomprises a protective material selected from the group consisting ofpolymeric materials, inorganic oxides, surfactants and mixtures thereofand further wherein the protective coating has a thickness of from about0.2 nm to about 100 nm.

In yet other embodiments, there is provided a magnetic ink comprising: asolvent carrier; an optional dispersant; an optional synergist; anoptional antioxidant; an optional viscosity controlling agent; anoptional colorant; an optional binder; and coated magnetic nanoparticlescomprising a magnetic metal core and a protective coating disposed onthe magnetic metal core, the coated magnetic nanoparticles beingdispersed in the solvent carrier and the protective coating is selectedfrom the group consisting of polymeric materials, inorganic oxides,surfactants and mixtures thereof, and further wherein the ink is usedfor Magnetic Ink Character Recognition (MICR) applications.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present embodiments, reference may behad to the accompanying figures.

FIG. 1 illustrates a cross-section of a coated magnetic nanoparticleaccording to the present embodiments;

FIG. 2 illustrates a cross-section of a coated magnetic nanoparticleaccording to an alternative embodiment to FIG. 1; and

FIG. 3 illustrates a cross-section of a coated magnetic nanoparticleaccording to an alternative embodiment to FIG. 1 or FIG. 2.

DETAILED DESCRIPTION

In the following description, it is understood that other embodimentsmay be utilized and structural and operational changes may be madewithout departure from the scope of the present embodiments disclosedherein.

Solvent ink technology broadens printing capability and customer baseacross many markets, and the diversity of printing applications will befacilitated by effective integration of printhead technology, printprocess and ink materials. As discussed above, while current ink optionsare successful for printing on various substrates, there is a need aless complicated method to produce magnetic solvent inks comprisingmagnetic metal nanoparticles which avoids the safety risks associatedwith the nanoparticles. In addition, solvent-based magnetic inks providefor enhanced robustness of the prints.

The present embodiments are directed generally to solvent-based magneticsolid inks. In particular, the present embodiments provide inks that aremade with coated magnetic metal nanoparticles dispersed in a solvent inkbase. One of the inherent properties of uncoated magnetic metalnanoparticles which precludes their use in the fabrication of commercialinks is their pyrophoric nature; uncoated (bare) magnetic nanoparticlesof a certain size, typically in the order of a few tens of nanometers orless, ignite spontaneously when exposed to oxygen in the ambientenvironment. For example, bare iron, cobalt and alloys nanoparticles area serious fire hazard. Thus, the present embodiments provide a safemethod for preparation of stable inks suitable for applications thatrequire the use of magnetic inks. The present embodiments provide coatedmagnetic metal nanoparticles which are protected from exposure to waterand air. These nanoparticles have a coating of various materials, suchas for example, carbon, polymers, inorganic oxides, surfactants, ormixtures thereof, which acts as a barrier to water or air.

Magnetic inks are required for two main applications: (1) Magnetic InkCharacter Recognition (MICR) for automated check processing and (2)security printing for document authentication. The resultingsolvent-based ink can be used for these applications. Moreover, asmentioned above, solid ink compositions are not normally designed formultiple passes across a magnetic reader. Thus, magnetic solid ink printmay wear off during the machine-reading process, either for MICR or fordocument authentication procedures. The present embodiments provide amagnetic ink that is solvent-based. More specifically, the ink of thepresent embodiments is made by dispersing coated magnetic metalnanoparticles in a solvent-based composition containing a solvent, anoptional viscosity controlling agent, an optional dispersant, anoptional synergist and optional binder. These solvent-based inkscomprising the coated magnetic nanoparticles are jetted as a liquiddispersion onto the print substrate. Because the ink is in a liquidstate when applied to the substrate, such as paper, the magnetic inkpenetrates into the substrate when printed. In contrast to conventionalsolid inks which sit on top of the substrate, the solvent carrier allowsthe ink of the present embodiments to penetrate the substrate coatingand fibers to ensure deposition of the ink components. As a result, theinks proved robust magnetic prints that can pass the machine-readingprocess steps of MICR or document authentication procedures, and beoverprinted with other ink types. The added robustness also removes theneed for adding a clear protective overcoat layer over the print, whichincreases the amount of ink used and adds to the pile height of theprinted documents.

The resulting solvent ink can also be applied using with piezoelectricinkjet print heads. Currently only water based MICR inkjet ink arecommercially available. Water based inks require special care of theprinthead to prevent evaporation of the ink or deposition of saltswithin the channel rendering the jetting ineffective. Furthermore highquality printing with aqueous inks generally requires specially treatedimage substrates. In addition, there is generally a concern with respectto possible incompatibility when operating both organic materials basedinks like solid, solvent or curable solid inks and water-based inkswithin the same printer. Issues like water evaporation due to theproximity to the organic heated ink tanks, rust, high humiditysensitivity of the organic inks are key problems which may preventimplementation of the water-based MICR solution. Thus, the presentembodiments further avoid these issues.

The present embodiments provide a solvent-based ink made from coatedmetal magnetic nanoparticles dispersed in a solvent-based ink base. Theprocess of ink fabrication comprise the following key steps: (1)preparation of a solvent solution containing appropriate dispersant andoptionally a synergist; (2) addition and breaking of solid aggregates ofthe coated nanoparticles (this step can be achieved by various processesincluding ball milling, attrition or high speed homogenizer mixing); (3)optional addition of viscosity controlling agents; and (4) filtration ofthe ink.

The inks are suitable for use in various applications, including MICRapplications. In addition, the printed inks may be used for decorationand for security printing purposes, even if the resulting inks do notsufficiently exhibit coercivity and remanence suitable for use in MICRapplications. The ink of the present disclosure exhibits stability,dispersion properties and magnetic properties that are superior to thatof an ink including magnetite.

The coated magnetic nanoparticles 5 are made of a core magneticnanoparticle 15 coated on the surface with a coating material 10 asshown in FIGS. 1-3. The coated magnetic nanoparticles can be produced tohave different shapes such as oval (FIG. 1), cubed (FIG. 2), andspherical (FIG. 3). The shapes are not limited to those depicted inthese three figures. Suitable coating materials may include a variety ofmaterials, including for example, polymers, inorganic oxides,surfactants and mixtures thereof. Polymeric materials may be selectedfrom the group consisting of amorphous, crystalline, polymers andoligomers with a low molecular weight (for example, a Mw of from about500 to about 5000, polymers with a high molecular weight (for example, aMw of from about 5000 to about 1,000,000), homopolymers, copolymers madeof one or more types of monomers, and the like, and mixtures thereof.Inorganic oxides may be selected from the group consisting of silica,titanium oxide, iron oxide, zinc oxide, aluminum oxide, and the like,and mixtures thereof. Surfactants may be selected from the groupconsisting of anionic, cationic, non-ionic, zwitterionic surfactants,and the like, and mixtures thereof. The magnetic ink is made bydispersing the coated nanoparticles in a solvent ink base. The coatingpresent on the surface of the nanoparticles provides air and moisturestability such that the nanoparticles are safe to handle. The amount ofthe different materials used in the coatings depends on the densities ofthe materials used. In general embodiments, the polymer may be presentin the coating in an amount of from about 0.1 to about 50 percent byweight of the total weight of the coating, the surfactant may be presentin the coating in an amount of from about 0.1 to about 30 percent byweight of the total weight of the coating, and the inorganic oxide maybe present in an amount of from about 0.5 to about 70 percent by weightof the total weight of the coating.

Solvent Carrier Material

The ink composition includes a carrier material, or a mixture of two ormore carrier materials. In the present embodiments, there is provided aliquid inkjet ink composition in which the carrier is one or moreorganic solvents.

In the present embodiments, the coated magnetic metal nanoparticles aredispersed into the solvent ink base. The solvent may be selected fromthe group consisting of isoparaffins like ISOPAR® manufactured by theExxon Corporation, hexane, toluene, methanol, ethanol, n-propanol,n-butanol, benzyl alcohol, methyl cellosolve, ethyl cellosolve, acetone,methyl ethyl ketone, cyclohexanone, chlorobenzene, methyl acetate,n-butyl acetate, dioxane, tetrahydrofuran, methylene chloride andchloroform, and mixtures and combinations thereof. Additionalcommercially available hydrocarbon liquids that may be used include, forexample, the NORPAR series available from Exxon Corporation, the SOLTROLseries available from the Phillips Petroleum Company, and the SHELLSOLseries available from the Shell Oil Company. In embodiments, the solventis present in the overall ink composition in an amount of from about 0.1to about 99 percent, or of from about 10 to about 90 percent, or of fromabout 30 to about 90 percent by weight of the total weight of the ink,although the specific amount can be outside of these ranges.

In embodiments, the ink exhibits a viscosity, typically on the order ofless than 15 centipoise (cP) or about 2 to 12 cP at jetting temperature(jetting temperature ranging from about 25° C. to about 140° C.

Coating Materials for Magnetic Metal Nanoparticles

Various materials may be used for the nanoparticle coating materials,for example, polymers, inorganic oxides, surfactants and mixturesthereof. The coating is disposed on the surface of the magnetic metalnanoparticles and may have a layer thickness of from about 0.2 nm toabout 100 nm, or from about 0.5 nm to about 50 nm, or from about 1 nm toabout 20 nm.

Polymers

Various polymers are suitable for producing protective coating layersfor the magnetic metal cores in nanoparticles. Suitable examples includePoly(methyl methacrylate) (PMMA), polystyrene, polyesters, and the like.Additional suitable polymer materials include, without limitation,thermoplastic resins, homopolymers of styrene or substituted styrenessuch as polystyrene, polychloroethylene, and polyvinyltoluene; styrenecopolymers such as styrene-p-chlorostyrene copolymer, styrene-propylenecopolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalenecopolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylatecopolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylatecopolymer, styrene-methyl methacrylate copolymer, styrene-ethylmethacrylate copolymer, styrene-butyl methacrylate copolymer,styrene-methyl α-chloromethacrylate copolymer, styrene-acrylonitrilecopolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethylether copolymer, styrene-vinyl methyl ketone copolymer,styrene-butadiene copolymer, styrene-isoprene copolymer,styrene-acrylonitrile-indene copolymer, styrene-maleic acid copolymer,and styrene-maleic acid ester copolymer; polymethyl methacrylate;polybutyl methacrylate; polyvinyl chloride; polyvinyl acetate;polyethylene; polypropylene; polyester; polyvinyl butyral; polyacrylicresin; rosin; modified rosin; terpene resin; phenolic resin; aliphaticor aliphatic hydrocarbon resin; aromatic petroleum resin; chlorinatedparaffin; paraffin wax, and the like. In embodiments, the protectivecoating comprises a polymer terminated with a functional group which isselected from a group of amide, amine, carboxylic acid, phosphine oxide,carboxyklic ester, alcohol, thiol. Polymers can be homopolymers orcopolymers, linear or branched, random and block copolymers. In furtherembodiments, oxygen barrier polymeric materials are particularlysuitable coating materials. Examples of oxygen barrier polymericmaterials include polyvinylidene chloride (PVDC), Ethylene Vinyl Alcohol(EVOH), High Density Polyethylene (HDPE), NYLON 6 and the like. Suitableoxygen barrier materials are also available from Dow Chemicals (SARANseries resins (e.g., SARAN 168 and SARAN 519)).

Copolymers are also suitable polymeric coating materials. For example, acopolymer made of PVDC and methyl acrylate monomers may be used forcoating. This copolymer is also available from Dow Chemicals (e.g.,SARAN XU 32019). Other examples include 10L Blend, SARAN XU 32019.39Blend and SARAN XU 32019.40 Blend. Additionally, some of the oxygenbarrier polymers, particularly copolymers of PVDC with otherco-monomers, are soluble in various solvents at various temperatures asshown in Table 1.

TABLE 1 Temperature at which polymer Polymer Material Solvent dissolves(° C.) PVDC homopolymer N-methylpyrrolidine 42 PVDC homopolymertetramethylene sufloxide 28 PVDC homopolymer N-acetylpiperidine 34 PVDCcopolymers tetrahydrofuran <60 PVDC copolymers 1,4-dioxane 50-100 PVDCcopolymers cyclohexanone 50-100

The polymer coating on magnetic nanoparticles provides stability againstair and moisture but also increases compatibility of the magneticparticles with the ink base due to the fact that both the polymercoating and the ink base are organic materials. Thus, this compatibilityresults in good dispersibility of the magnetic nanoparticles as comparedto bare magnetic metal nanoparticles. As a result, there may besituations when, depending on the actual ink base components and thetype of polymer, a synergist or dispersant may not be required at all orthe amount needed is significantly decreased, thus saving extracomponents and costs.

Generally, the process of ink fabrication comprise a few main steps: (1)prepare a solvent solution containing an appropriate dispersant andoptionally a synergist; (2) addition and breaking of solid aggregates ofpolymer-coated nanoparticles, which can be achieved by variousprocesses, including but not limited to, ball milling, attrition or highspeed homogenizer mixing; (3) optionally adding viscosity controllingagents; and (4) filtration of the ink. Methods for fabrication of thepolymer coated nanoparticles and particularly suitable for magneticnanoparticle coating are known and some representative examplesdescribed below.

Coatings and methods for coating particles with polymers layers aredescribed in, for example, Caruso, F., Advanced Materials, 13: 11-22(2001). Polymer coated nanoparticles can be obtained via synthetic andnon synthetic routes: polymerization of the particle surface; adsorptiononto the particles; surface modifications via polymerization processes;self-assembled polymer layers; inorganic and composite coatingsincluding precipitation and surface reactions and controlled depositionof preformed inorganic colloids; and use of biomacromolecular layer inspecific applications. A number of techniques for the preparation ofmagnetic nano- and micronized particles are also described in Journal ofSeparation Science, 30: 1751-1772 (2007). Polystyrene-coated cobaltnanoparticles are described in U.S. Publication No. 2010/0015472 toBradshaw, which is hereby incorporated by reference. The disclosedprocess consists of thermal decomposition of dicobalt octacarbonyl indichlorobenzene as a solvent in the presence of a polystyrene polymerterminated with a phosphine oxide group and an amine terminatedpolystyrene, at 160° C. under argon. The process provided magneticcobalt nanoparticles having a polymer coating including a polystyreneshell. Additionally, other polymer shells can be placed on the surfaceof the coated cobalt nanoparticles by exchange of the originalpolystyrene shell with other polymers. The reference further describesreplacement of the polystyrene shell on coated nanoparticles bypolymethylmethacrylate shell, through exchange reaction with polymethylmethacrylate (PMMA) in toluene. These polymer coated magneticnanoparticle materials are also suitable for fabrication of magneticinks. U.S. Publication No. 2007/0249747 to Tsuji et al. disclosesfabrication of polymer-coated metal nanoparticles from magnetic FePtnanoparticles of a particle size of about 4 nm by stirring FePtnanoparticle dispersion in the presence of a —SH terminated polymer.Suitable polymers include, for example PMMA.

The surface of magnetic nanoparticles can be modified: by grafting; atomtransfer radical polymerization (ATRP) and reversibleaddition-fragmentation chain transfer (RAFT) polymerization techniques(the latter using a chain transfer agent but no metal catalyst); solventevaporation method; layer by layer process; phase separation method;sol-gel transition; precipitation technique; heterogeneouspolymerization in the presence of magnetic particles;suspension/emulsion polymerization; microemulsion polymerization; anddispersion polymerization.

In addition to the known methods described above, a number of specifictechniques are of interest, such as for example, use of sonochemistryfor chemical grafting of anti-oxidant molecules with additionalhydrophobic polymer coating directly onto TiO₂ particle surfaces (Chem.Commun., 4815-4817 (2007)); use of pulse-plasma techniques (J. ofMacromolecular Science, Part B: Physics, 45: 899-909 (2006)); use ofsupercritical fluids and anti-solvent process for coating/encapsulationof microparticles with a polymer (J. of Supercritical Fluids, 28: 85-890(2004)); and use of electrohydrodynamic atomization for the productionof narrow-size-distribution polymer-pigment-nanoparticle composites.

Encapsulation/coating and surface modifications of nanoparticles, andparticularly magnetic nanoparticles with polymers, also provide usefulmethods that can be used to fabricate the ink of the presentembodiments. For example, polymer-coated iron nanoparticles may beformed by thermal decomposition of iron pentacarbonyl in a solvent inthe presence of a modified polymer structure with a terminal anchoringgroup, tetraethylenepentaamine (TEPA) (Burke et al., Chemical Materials,14: 4752-61 (2002)). After filtration and solvent removal, thecore-shell iron nanoparticles contain a shell made out of the polymericmaterial, for example, polyisobutylene (PIB), polystyrene (PS), andpolyethylene (PE). Polystyrene coated nanoparticles may be obtained bythermal decomposition of iron carbonyl gas in the presence of styrenemonomer by using plasma polymerization techniques (Srikanth et al.,Applied Physics Letters, 79: 3503-5 (2001)). The plasma generated heatinitiates fast decomposition of the iron carbonyl while at the same timethe styrene breaks down forming free radicals which initiate thepolymerization process on the surface of the generated ironnanoparticles.

All of the above literature are hereby incorporated by reference intheir entirety as disclosing methods for providing polymer coatedmagnetic nanoparticles.

Inorganic Oxides

Suitable inorganic oxides for use as coating materials include silica,titania, iron oxide, aluminum oxide, zinc oxide and other similarinorganic oxides and mixtures thereof.

Generally, the process of ink fabrication comprise a few main steps: (1)prepare a solvent solution containing an appropriate dispersant andoptionally a synergist; (2) addition and breaking of solid aggregates ofinorganic oxide-coated nanoparticles, which can be achieved by variousprocesses, including but not limited to, ball milling, attrition or highspeed homogenizer mixing; (3) optionally adding viscosity controllingagents; and (4) filtration of the ink. Methods for fabrication of theinorganic oxide coated nanoparticles and particularly suitable formagnetic nanoparticle coating are known and some representative examplesdescribed below.

Methods for fabrication of such core-shell particles having a protectivelayer (shell) made out of inorganic oxide are described in, for example,U.S. Patent Publication No. 2010/0304006, which describes a methodwherein the silica coating on the surface of metal nanoparticles isprovided by catalytic hydrolysis of a tetraalkoxysilane on the surfaceof metal nanoparticles. In order to avoid direct access of water to thesurface of the metal nanoparticles, the process is carried in a mediumcontaining an organic solvent like tetrahydrofuran (THF), in presence ofonly the required amount of water needed for hydrolysis/condensation ofthe silica precursor. Coated magnetic nanoparticles made by this methodinclude Fe, Fe/Co alloys.

Bomati-Miguel et al., Journal of Magnetism and Magnetic Materials,290-291: 272-275 (2005) describes one-step fabrication of silica coatediron nanoparticles by a continuous process involving laser-inducedpyrolysis of ferrocene (the source of iron metal) and TEOS aerosols (thesource of siloxane protective coating).

Ni et al., Materials Chemistry and Physics, 120: 206-212 (2010) reporteddeposition of a silica layer on iron nanoparticles dispersed in ethanolsolution containing tetraethyl orthosilicate (TEOS) in presence ofcatalytic amounts of a solution of ammonia.

The general procedure for fabrication of metal oxide coated magneticmetal nanoparticles is based on controlled partial oxidation of the toplayers of magnetic metal nanoparticles. For example, as disclosed inTurgut, Z et al., Journal of Applied Physics, 85 (8, Pt. 2A): 4406-4408(1999), a thin iron oxide/cobalt oxide coating layer on FeConanoparticles was prepared by controlled oxidation of metal precursorsparticles with a plasma torch (Turgut, Z et al., Journal of AppliedPhysics (1999), 85(8, Pt. 2A), 4406-4408).

All of the above literature are hereby incorporated by reference intheir entirety as disclosing methods for providing inorganicoxide-coated magnetic nanoparticles.

Surfactants

Various surfactants can be present on the surface of the magnetic metalnanoparticles. Examples include oleic acid, trioctyl phosphine oxide(TOPO), 1-butanol, tributyl phosphine, CTAB (ammonium salt), oleylphosphine and others. Additional suitable surfactants include betahydroxy carboxylic acids and their esters containing long linear, cyclicor branched aliphatic chains, such as those having about 5 to about 60carbons, such as pentyl, hexyl, cyclohexyl, heptyl, octyl, nonyl, decyl,undecyl, and the like; sorbitol esters with long chain aliphaticcarboxylic acids such as lauric acid, oleic acid (SPAN® 85), palmiticacid (SPAN® 40), and stearic acid (SPAN® 60); polymeric compounds suchas polyvinylpyrrolidone, poly(1-vinylpyrrolidone)-graft-(1-hexadecene),poly(1-vinylpyrrolidone)-graft-(1-triacontene), poly(1vinylpyrrolidone-co-acrylic acid), and combinations thereof. Inembodiments, the surfactant is selected from the group consisting ofoleic acid, lauric acid, palmitic acid, stearic acid, hexyl phosphonicacid, trioctyl phosphine oxide (TOPO), 1-butanol, tributyl phosphine andoleyl phosphine, oleyl amine, polymeric compounds likepolyvinylpyrrolidone, poly(1-vinylpyrrolidone)-graft-(1-hexadecene),poly(1-vinylpyrrolidone)-graft-(1-triacontene), poly(1vinylpyrrolidone-co-acrylic acid), pentyl, hexyl, cyclohexyl, heptyl,octyl, nonyl, decyl, or undecyl beta-hydroxy carboxylic acid, sorbitolesters with long chain carboxylic acid and combinations thereof.Typically the surfactant-coated nanoparticles are provided by performingthe fabrication of metal nanoparticles from metal precursors, in thepresence of a suitable surfactant in a solvent.

In embodiments, where the protective coating comprises a surfactant, theink may consist only of the organic solvent carrier, and coated magneticnanoparticles, without the need for other additives.

Generally, the process of ink fabrication comprise a few main steps: (1)prepare a solvent solution containing an appropriate dispersant andoptionally a synergist; (2) addition and breaking of solid aggregates ofsurfactant-coated nanoparticles, which can be achieved by variousprocesses, including but not limited to, ball milling, attrition or highspeed homogenizer mixing; (3) optionally adding viscosity controllingagents; and (4) filtration of the ink.

Methods for fabrication of the surfactant coated nanoparticles andparticularly suitable for magnetic nanoparticle coating are known andsome representative examples described below.

Suitable methods providing surfactant coated magnetic metalnanoparticles in solvent include metal salts reduction by borohydrides(I. Guo et al. Phys. Chem. Chem. Phys., 3: 1661-5 (2001); reduction ofmetal salts by polyols (G. S. Chaubey et al., J. Am. Chem. Soc., 120:7214-5 (2007)); and thermal decomposition of metal carbonyls (U.S. Pat.No. 7,407,572).

For example, in a typical process of reduction of metal salts byborohydrides, nanodroplets (or reverse micelles) containing watersoluble metal salts in water are dispersed in an organic solvent. Themetal salts are subsequently reduced to the metal form (degree ofoxidation is zero) by borohydride ions present in the nanodroplet. Thisprocess provides stabilized surfactant coated metal nanoparticles.

Typical metal precursors include Fe(II) and Co(II) salts like FeCl₂ orCoCl₂. Various surfactants have been demonstrated including 1-butanol,higher MW alcohols, oleic acid, CTAB (ammonium salt) and oleylphosphine.

Another method that can be used to provide surfactant coated metalnanoparticles is through the reduction of metal salts by polyols. Withthis method, a metal salt is reduced by a polyol when the mixture isheated at temperatures of about from about 200 to about 300° C. (C. B.Murray et al., MRS Bull. 985 (2001); G. S. Chaubey et al., J. Am. Chem.Soc., 120: 7214-5 (2007); B. Martorana et al., Sensors and Actuators A129: 176-9 (2006)). An exemplary reaction scheme is shown below:

Suitable known metal precursors include Co(OH)₂, Fe(OH)₂ or precursorsin presence of hydroxides such as Co(Acetate)₂×4H2O, FeCl₂×4H2O,Co(acac)₂, Fe(acac)₃. Typical polyols include tetraethylene glycol,trimethylene glycol (TMG), diethylene glycol (DEG), ethylene glycol(EG), propylene glycol, and 1,2-propanediol.

Another method that can be used to provide surfactant coated metalnanoparticles is through thermal decomposition of metal carbonyls, Inthis process, a metal carbonyl is heated to decompose and generate metalnanoparticles coated with a surfactant present in the solution (U.S.Pat. No. 7,407,572; V. F. Puntes et al., Science, 291: 2115 (2001); S.J. Park et al., J. Am. Chem. Soc. 122: 8581-2 (2000)). An exemplaryreaction scheme is shown below:

All of the above literature is hereby incorporated by reference in theirentirety as disclosing methods for providing surfactant-coated magneticnanoparticles.

Magnetic Material

In embodiments, two types of magnetic metal based inks can be obtainedby the process herein, depending on the particle size and shape:ferromagnetic ink and superparamagnetic ink

In embodiments, the metal nanoparticles herein can be ferromagnetic.Ferromagnetic inks become magnetized by a magnet and maintain somefraction of the saturation magnetization once the magnet is removed. Themain application of this ink is for Magnetic Ink Character Recognition(MICR) used for checks processing.

In embodiments, the metal nanoparticles herein can be superparamagneticinks. Superparamagnetic inks are also magnetized in the presence of amagnetic field but they lose their magnetization in the absence of amagnetic field. The main application of superparamagnetic inks is forsecurity printing, although not limited. In this case, an inkcontaining, for example, magnetic particles as described herein andcarbon black appears as a normal black ink but the magnetic propertiescan be detected by using a magnetic sensor or a magnetic imaging device.Alternatively, a metal detecting device may be used for authenticatingthe magnetic metal property of secure prints prepared with this ink. Aprocess for superparamagnetic image character recognition (i.e. usingsuperparamagnetic inks) for magnetic sensing is described in U.S. Pat.No. 5,667,924, which is hereby incorporated by reference herein in itsentirety.

As described above, the metal nanoparticles herein can be ferromagneticor superparamagnetic. Superparamagnetic nanoparticles have a remanentmagnetization of zero after being magnetized by a magnet. Ferromagneticnanoparticles have a remanent magnetization of greater than zero afterbeing magnetized by a magnet; that is, ferromagnetic nanoparticlesmaintain a fraction of the magnetization induced by the magnet. Thesuperparamagnetic or ferromagnetic property of a nanoparticle isgenerally a function of several factors including size, shape, materialselection, and temperature. For a given material, at a giventemperature, the coercivity (i.e. ferromagnetic behaviour) is maximizedat a critical particle size corresponding to the transition frommultidomain to single domain structure. This critical size is referredto as the critical magnetic domain size (Dc, spherical). In the singledomain range there is a sharp decrease of the coercivity and remanentmagnetization when decreasing the particle size, due to thermalrelaxation. Further decrease of the particle size results in completeloss of induced magnetization because the thermal effect become dominantand are sufficiently strong to demagnetize previously magneticallysaturated nanoparticles. Superparamagnetic nanoparticles have zeroremanence and coercivity. Particles of a size of about and above the Dcare ferromagnetic. For example, at room temperature, the Dc for iron isabout 15 nanometers for fcc cobalt is about 7 nanometers and for Nickelthe value is about 55 nm. Further, iron nanoparticles having a particlesize of 3, 8, and 13 nanometers are superparamagnetic while ironnanoparticles having a particle size of 18 to 40 nanometers areferromagnetic. For alloys, the Dc value may change depending on thematerials. For additional discussion of such details, see U.S. PatentPublication No. 20090321676 to Breton et al.; Burke, et al., Chemistryof Materials, pp. 4752-4761 (2002); B. D. Cullity and C. D. Graham,Introduction to Magnetic Materials, IEEE Press (Wiley), 2^(nd) Ed.,Chapter 11, Fine Particles and Thin Films, pp. 359-364 (2009); Lu et al.Angew. Chem. Int. Ed. 46:1222-444 (2007), Magnetic Nanoparticles:Synthesis, Protection, Functionalization and Application, which are allhereby incorporated by reference herein in their entirety.

In embodiments, the nanoparticles may be a magnetic metallicnanoparticle, that includes, for example, Co and Fe (cubic), amongothers. Others magnetic core materials include Mn, Ni and/or alloys madeof all of the foregoing and other magnetic metals like rare earthmetals. Additionally, the magnetic nanoparticles may be bimetallic ortrimetallic, or a mixture thereof. Examples of suitable bimetallicmagnetic nanoparticles include, without limitation, CoPt, fcc phaseFePt, fct phase FePt, FeCo, MnAl, MnBi, mixtures thereof, and the like.Examples of trimetallic nanoparticles can include, without limitationtri-mixtures of the above magnetic nanoparticles, or core/shellstructures that form trimetallic nanoparticles such as Co-covered fctphase FePt.

The magnetic nanoparticles may be prepared by any method known in theart, including ball-milling attrition of larger particles (a commonmethod used in nano-sized pigment production), followed by annealing.The annealing is generally necessary because ball milling producesamorphous nanoparticles, which need to be subsequently crystallized intothe required single crystal form. The nanoparticles can also be madedirectly by RF plasma. Appropriate large-scale RF plasma reactors areavailable from Tekna Plasma Systems (Sherbrooke, Québec). Thenanoparticles can also be made by a number of in situ methods insolvents in presence of suitable coating materials like surfactants.

The average particle size of the magnetic nanoparticles may be, forexample, about 3 nm to about 300 nm in size in all dimensions. They canbe of any shape including spheres, cubes and hexagons. In oneembodiment, the nanoparticles are about 5 nm to about 500 nm in size,such as from about 10 nm to about 300 nm, or from 20 nm to about 250 nm,although the amount can be outside of these ranges. Herein, “average”particle size is typically represented as d₅₀, or defined as the medianparticle size value at the 50^(th) percentile of the particle sizedistribution, wherein 50% of the particles in the distribution aregreater than the d₅₀ particle size value, and the other 50% of theparticles in the distribution are less than the d₅₀ value. Averageparticle size can be measured by methods that use light scatteringtechnology to infer particle size, such as Dynamic Light Scattering. Theparticle diameter refers to the length of the pigment particle asderived from images of the particles generated by Transmission ElectronMicroscopy (TEM) or from Dynamic Light Scattering measurements.

The magnetic nanoparticles may be in any shape. Exemplary shapes of themagnetic nanoparticles can include, for example, without limitation,needle-shape, granular, globular, platelet-shaped, acicular, columnar,octahedral, dodecahedral, tubular, cubical, hexagonal, oval, spherical,densdritic, prismatic, amorphous shapes, and the like. An amorphousshape is defined in the context of the present invention as anill-defined shape having recognizable shape. For example an amorphousshape has no clear edges or angles. The ratio of the major to minor sizeaxis of the single nanocrystal (D_(major)/D_(minor)) can be less thanabout 10:1, such as from about less than about 3:2, or less than about2:1.

The loading requirements of the magnetic nanoparticles in the ink may befrom about 0.5 weight percent to about 30 weight percent, such as fromabout 5 weight percent to about 10 weight percent, or from about 6weight percent to about 8 weight percent, although the amount can beoutside of these ranges.

The magnetic nanoparticle can have a remanence of about 20 emu/g toabout 100 emu/g, such as from about 30 emu/g to about 80 emu/g, or about50 emu/g to about 70 emu/g, although the amount can be outside of theseranges.

The coercivity of the magnetic nanoparticle can be, for example, about200 Oersteds to about 50,000 Oersteds, such as from about 1,000 Oerstedsto about 40,000 Oersteds, or from about 10,000 Oersteds to about 20,000Oersteds, although the amount can be outside of these ranges.

The magnetic saturation moment may be, for example, about 20 emu/g toabout 150 emu/g, such as from about 30 emu/g to about 120 emu/g, or fromabout 40 emu/g to about 80 emu/g, although the amount can be outside ofthese ranges.

Examples of suitable magnetic nanoparticle compositions with largemagnetocrystalline anisotropy, K1 and which are suitable for coatingwith protective coatings are disclosed in U.S. Patent Publication No.20090321676, which is hereby incorporated by reference in its entirety.

Binder Resin

The ink composition according to the present disclosure may also includeone or more binder resins. The binder resin may be any suitable agent.Suitable binder resins include, without limitation, a maleic modifiedrosin ester (BECKACITE 4503 resin from Arizona chemical company),phenolics, maleics, modified phenolics, rosin ester, modified rosin,phenolic modified ester resins, rosin modified hydrocarbon resins,hydrocarbon resins, terpene phenolic resins, terpene modifiedhydrocarbon resins, polyamide resins, tall oil rosins, polyterpeneresins, hydrocarbon modified terpene resins, acrylic and acrylicmodified resins and similar resins or rosin known to be used in printinginks, coatings and paints, and the like.

Other suitable binder resins include, without limitation, thermoplasticresins, homopolymers of styrene or substituted styrenes such aspolystyrene, polychloroethylene, and polyvinyltoluene; styrenecopolymers such as styrene-p-chlorostyrene copolymer, styrene-propylenecopolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalenecopolymer, styrene-methylacrylate copolymer, styrene-ethylacrylatecopolymer, styrene-butylacrylate copolymer, styrene-octylacrylatecopolymer, styrene-methylmethacrylate copolymer,styrene-ethylmethacrylate copolymer, styrene-butylmethacrylatecopolymer, styrene-methyl-α-chloromethacrylate copolymer,styrene-acrylonitrile copolymer, styrene-vinylmethyl ether copolymer,styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketonecopolymer, styrene-butadiene copolymer, styrene-isoprene copolymer,styrene-acrylonitrile-indene copolymer, styrene-maleic acid copolymer,and styrene-maleic acid ester copolymer; polymethylmethacrylate;polybutylmethacrylate; polyvinyl chloride; polyvinyl acetate;polyethylene; polypropylene; polyester; polyvinyl butyral; polyacrylicresin; rosin; modified rosin; terpene resin; phenolic resin; aliphaticor aliphatic hydrocarbon resin; aromatic petroleum resin; chlorinatedparaffin; paraffin wax, and the like. These binder resins can be usedalone or in combination.

The molecular weight, molecular weight distribution, cross-linkingdegree and other properties of each of the above binder resins areselected in accordance with the desired melt viscosity of the ink to beobtained.

One or more waxes may be added to the MICR inkjet ink in order to raisethe image optical density and to effectively prevent the offset to areading head and the image smearing. The wax can be present in an amountoil, for example, from about 0.1 to about 10 weight percent, or fromabout 1 to about 6 weight percent based on the total weight of the inkcomposition, although the amount can be outside of these ranges.Examples of suitable waxes include, but are not limited to, polyolefinwaxes, such as low molecular weight polyethylene, polypropylene,copolymers thereof and mixtures thereof. Other examples include apolyethylene wax, a polypropylene wax, a fluorocarbon-based wax, orFischer-Tropsch wax, paraffin, and bio-derived wax although other waxescan also be used. The wax may, for example, help prevent offset to areading head and image smearing.

Colorants

The MICR ink as prepared is either black or dark brown. In furtherembodiments, the MICR ink according to the present disclosure may befurther produced as a colored ink by adding a colorant during inkproduction. Alternatively, a MICR ink lacking a colorant may be printedon a substrate during a first pass, followed by a second pass, wherein acolored ink that is lacking MICR particles is printed directly over thecolored ink, so as to render the colored ink MICR-readable. This can beachieved through any means known in the art. For example, each ink canbe stored in a separate reservoir. The printing system delivers each inkseparately to the substrate, and the two inks interact. The inks may bedelivered to the substrate simultaneously or consecutively. Any desiredor effective colorant can be employed in the ink compositions, includingpigment, dye, mixtures of pigment and dye, mixtures of pigments,mixtures of dyes, and the like. The coated magnetic nanoparticles mayalso, in embodiments, impart some or all of the colorant properties tothe ink composition.

Suitable colorants for use in the MICR ink according to the presentdisclosure include, without limitation, carbon black, lamp black, ironblack, ultramarine, Nigrosine dye, Aniline Blue, Du Pont Oil Red,Quinoline Yellow, Methylene Blue Chloride, Phthalocyanine Blue,Phthalocyanine Green, Rhodamine 6C Lake, Chrome Yellow, quinacridone,Benzidine Yellow, Malachite Green, Hansa Yellow C, Malachite Greenhexalate, oil black, azo oil black, Rose Bengale, monoazo pigments,disazo pigments, trisazo pigments, tertiary-ammonium salts, metallicsalts of salicylic acid and salicylic acid derivatives, Fast Yellow G3,Hansa Brilliant Yellow 5GX, Disazo Yellow AAA, Naphthol Red HFG, LakeRed C, Benzimidazolone Carmine HF3CS, Dioxazine Violet, BenzimidazoloneBrown HFR. Aniline Black, titanium oxide, Tartrazine Lake, Rhodamine 6GLake, Methyl Violet Lake, Basic 6G Lake, Brilliant Green lakes, HansaYellow, Naphtol Yellow, Watching Red, Rhodamine B, Methylene Blue,Victoria Blue, Ultramarine Blue, and the like.

The amount of colorant can vary over a wide range, for instance, fromabout 0.1 to about 50 weight percent, or from about 3 to about 20 weightpercent, and combinations of colorants may be used.

Viscosity Controlling Agent

In particular embodiments, the viscosity controlling agent may beselected from the group consisting of aliphatic ketones, such asstearone, and the like, polymers such as polystyrene,polymethylmethacrylate, and the like, and thickening agents such asthose available from BYK Chemie. When present, the optional viscositymodifier is present in the ink in any desired or effective amount, suchas from about 0.1 to about 99 percent by weight of the ink.

Antioxidant

The ink composition can also optionally contain an antioxidant. Theoptional antioxidants of the ink compositions protect the images fromoxidation and also protect the ink components from oxidation during theheating portion of the ink preparation process. Specific examples ofsuitable antioxidants include NAUGUARD® series of antioxidants such asNAUGUARD® 445, NAUGUARD® 524, NAUGUARD® 76, and NAUGUARD® 512(commercially available from Chemtura Corporation (Philadelphia, Pa.)),the IRGANOX® series of antioxidants such as IRGANOX® 1010 (commerciallyavailable from BASF), and the like. When present, the optionalantioxidant can be present in the ink in any desired or effectiveamount, such as in an amount of from at least about 0.01 to about 20percent by weight of the ink, such as about 0.1 to about 5 percent byweight of the ink, or from about 1 to about 3 percent by weight of theink, although the amount can be outside of these ranges.

Viscosity Modifier

The ink composition can also optionally contain a viscosity modifier.Examples of suitable viscosity modifiers include aliphatic ketones, suchas stearone, and the like, polymers such as polystyrene,polymethylmethacrylate, thickening agents such as those available fromBYK Chemie, and others. When present, the optional viscosity modifiercan be present in the ink in any desired or effective amount, such asabout 0.1 to about 99 percent by weight of the ink, such as about 1 toabout 30 percent by weight of the ink, or about 10 to about 15 percentby weight of the ink, although the amount can be outside of theseranges.

Dispersants

Dispersant may be optionally present in then ink formulation. The roleof the dispersant is to further ensure improved dispersion stability ofthe coated magnetic nanoparticles by stabilizing interactions with thecoating material. Suitable dispersant include surfactants typically usedin various solvent-based processes including, but not limited to, oleicacid, oleyl amine, trioctyl phosphine oxide (TOPO), hexyl phosphonicacid (HPA); polyvinylpyrrolidone (PVP), block copolymer dispersantscomprising pigment-philic block and solvent-philic block, such as thosesold under the name SOLSPERSE® such as Solsperse® 16000, Solsperse®28000, Solsperse® 32500, Solsperse® 38500, Solsperse® 39000, Solsperse®54000, Solsperse® 17000, Solsperse® 17940 from Lubrizol Corporation,beta-hydroxy carboxylic acids and their esters containing long linear,cyclic or branched aliphatic chains, such as those having about 5 toabout 60 carbons, such as pentyl, hexyl, cyclohexyl, heptyl, octyl,nonyl, decyl, undecyl, and the like; sorbitol esters with long chainaliphatic carboxylic acids such as lauric acid, oleic acid (SPAN® 85),palmitic acid (SPAN® 40), and stearic acid (SPAN® 60); polymericcompounds such as polyvinylpyrrolidone,poly(1-vinylpyrrolidone)-graft-(1-hexadecene),poly(1-vinylpyrrolidone)-graft-(1-triacontene),poly(1-vinylpyrrolidone-co-acrylic acid), and combinations thereof. Inembodiments, the dispersant is selected from the group consisting ofoleic acid, lauric acid, palmitic acid, stearic acid, trioctyl phosphineoxide, hexyl phosphonic acid, polyvinylpyrrolidone,poly(1-vinylpyrrolidone)-graft-(1-hexadecene),poly(1-vinylpyrrolidone)-graft-(1-triacontene),poly(1-vinylpyrrolidone-co-acrylic acid), pentyl, hexyl, cyclohexyl,heptyl, octyl, nonyl, decyl, or undecyl beta-hydroxy carboxylic acid,and combinations thereof. Further examples of suitable dispersants mayinclude Disperbyk 108, Disperbyk 116, (ex Byk) Borch GEN 911, Ircopserse2153 and 2155 (ex Lubrizol), acid and acid ester waxes from Clariant,for example Licowax S. Suitable dispersants are described in pendingapplications U.S. patent application Ser. No. 12/641,564, filed Dec. 18,2009, U.S. patent application Ser. No. 12/891,619, filed Sep. 27, 2010,and U.S. Patent Publication No. 2010/0292467, the entireties of whichare hereby incorporated by reference.

The dispersant may be the same or different when compared with thesurfactant present, in some embodiments, on the surface of the particleprior to ink preparation.

A suitable amount of dispersant can be selected, such as in an amount ofabout 0.1 to about 20 weight percent, such as from about 0.5 to about 12weight percent of the ink weight, although the amount can be outside ofthese ranges. The choice of particular dispersants or combinationsthereof as well as the amounts of each to be used are within the purviewof those skilled in the art.

Synergist

Specific examples of commercially available synergists includeSolsperse® 22000 and Solsperse® 5000 (Lubrizol Advance Materials, Inc.).Although in embodiments where the surface coating comprises surfactants,the dispersant and/or synergist may not be needed. Thus, selection ofthe dispersant and/or synergist depends on the type of protectivecoating.

Preparation of Ink

The ink composition of the present disclosure can be prepared by anydesired or suitable method. For example, the ink ingredients can bemixed together, followed by heating, typically to a temperature of fromabout 50° C. to about 140° C., although the temperature can be outsideof this range, and stirring until a homogeneous ink composition isobtained, followed by cooling the ink to ambient temperature (typicallyfrom about 20° C. to about 25° C.). Other methods for making inkcompositions are known in the art and will be apparent based on thepresent disclosure.

Printing of the Ink

The magnetic metal particle ink may generally be printed on a suitablesubstrate such as, without limitation, paper, glass art paper, bondpaper, paperboard, Kraft paper, cardboard, semi-synthetic paper orplastic sheets, such as polyester or polyethylene sheets, and the like.These various substrates can be provided in their natural state, such asuncoated paper, or they can be provided in modified forms, such ascoated or treated papers or cardboard, printed papers or cardboard, andthe like.

Specific suitable papers include plain papers such as XEROX 4200 papers,XEROX Image Series papers, ruled notebook paper, bond paper, silicacoated papers such as Sharp Company silica coated paper, JuJo paper,HAMMERMILL LASERPRINT paper, and the like, glossy coated papers such asXEROX Digital Color Gloss, Sappi Warren Papers LUSTROGLOSS, specialtypapers such as Xerox DURAPAPER, and the like.

Further suitable materials may be used, including but not limited to,transparency materials, fabrics, textile products, plastics, polymericfilms, inorganic recording mediums such as metals and wood, and thelike, transparency materials, fabrics, textile products, plastics,polymeric films, inorganic substrates such as metals and wood, and thelike.

For printing the ink on a substrate, any suitable printing method may beused. For example, suitable methods include, without limitation,roll-to-roll high volume analog printing methods, such as gravure,rotogravure, flexography, lithography, etching, screenprinting, and thelike. Additionally, thermography, inkjet printing, or a combinationthereof may, be used. The ink may also be used with piezo type inkjetprint heads suitable for both low and high temperature operation andordinary instrument for writing. In a particular embodiment, the methodused is inkjet printing.

The ink of the present disclosure may be used in both MICR and non-MICRapplications.

The inks described herein are further illustrated in the followingexamples. All parts and percentages are by weight unless otherwiseindicated.

It will be appreciated that various of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also,various presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art, and are also intended to beencompassed by the following claims.

While the description above refers to particular embodiments, it will beunderstood that many modifications may be made without departing fromthe spirit thereof. The accompanying claims are intended to cover suchmodifications as would fall within the true scope and spirit ofembodiments herein.

The presently disclosed embodiments are, therefore, to be considered inall respects as illustrative and not restrictive, the scope ofembodiments being indicated by the appended claims rather than theforegoing description. All changes that come within the meaning of andrange of equivalency of the claims are intended to be embraced therein.

EXAMPLES

The examples set forth herein below and are illustrative of differentcompositions and conditions that can be used in practicing the presentembodiments. All proportions are by weight unless otherwise indicated.It will be apparent, however, that the present embodiments can bepracticed with many types of compositions and can have many differentuses in accordance with the disclosure above and as pointed outhereinafter.

Example 1 Preparation of Solvent-Based Magnetic Ink with Polymer-CoatedNanoparticles

1.a. Polymer coated nanoparticles: Polystyrene coated cobalt,nanoparticles are obtained by thermal decomposition of dicobaltoctacarbonyl in dichlorobenzene as a solvent in the presence of apolystyrene polymer terminated with a phosphine oxide group, and anamine terminated polystyrene in a ratio of 4:1 (w/w) at 160 deg. C.under argon for 30 min. The reaction mixture is precipitated into hexaneand further washed to provide polystyrene coated cobalt nanoparticles.The fabrication process is described in US2010/0015472 A1 (Bradshaw).

1.b. Solvent ink with polymer coated nanoparticles: A 30 ml brown bottleis filled with 10 g of ISOPAR M (solvent), 0.180 g of SOLSPERSE 5000 and0.80 g of SOLSPERSE 17000. To this mixture are added 2.5 g ofpolymer-coated cobalt nanoparticles as described in US2010/0015472. Thesolution is mixed with an IKA KS130 shaker to ensure wetting of thepolymer-coated cobalt aggregates (3 hours). 70 g of pre-cleaned ⅛ inchdiameter zirconia balls are added and the composition is ball-milled for1-7 days in order to induce de-agglomeration of the polymer-coatedmagnetic nanoparticles. The process produced an ink havingwell-dispersed magnetic nanoparticles.

Example 2 Preparation of Solvent-Based Magnetic Ink withSurfactant-Coated Nanoparticles

2.a. Surfactant coated FeCo alloy magnetic nanoparticles of an averagesize of about 10 nm (as determined by TEM) are obtained by reductivedecomposition of Fe(III) acetylacetonate and Co(II) acetylacetonate in amixture of surfactants (oleic acid and trioctyl phosphine) in1,2-hexadecanediol under a gas mixture of 93% Ar+7% H₂ at 300° C., Theexperimental procedure is fully described in J. Am. Chem. Soc. 120:7214-5 (2007).

The procedure for preparation of a solvent based magnetic ink fromExample 1.b. is repeated with surfactant-coated magnetic nanoparticlesdescribed above instead of polymer-coated magnetic nanoparticles.

The process produced an ink having well dispersed magneticnanoparticles.

Example 3 Preparation of Solvent-Based Magnetic Ink with InorganicOxide-Coated Nanoparticles

Silica coated iron nanoparticles of an average particle size of 300 nmare synthesized by reduction of FeCl₃·6H₂O with NaOH/N₂H₄·H₂O reducingagent. After washing with ethanol, a silica coating is deposed by usingthe Stöber method. In this procedure, the silica layer is deposed from atetraethyl orthosilicate precursor, which is hydrolyzed in anammonia/water mixture at apH of 8-9 for 4 hours at 40° C. The procedurefor fabrication of silica coated iron nanoparticles is fully describedby Ni et al., in Materials Chemistry and Physics 10: 206-212 (2010).

The procedure for preparation of a solvent based magnetic ink fromExample 1.b. is repeated with silica-coated magnetic nanoparticlesdescribed above instead of polymer-coated magnetic nanoparticles.

For all of the above examples, a convenient and effective method for theparticle size reduction of organic pigments and even carbon black is byattrition using suitable media with optional heating. The attritionprocess typically provides higher energy input compared to therelatively small ball-milling scale. The attrition process may be usedas a more efficient way for providing well dispersed (de-agglomerated)magnetic nanoparticles in the solvent ink vehicle.

SUMMARY

Solvent magnetic ink compositions made by using polymer, surfactant, orinorganic oxide coated magnetic nanoparticles dispersed in solvent inkbase and optional additives, as described herein, provides robustmagnetic solvent inks useful for applications like MICR applications.The robust magnetic prints made with these inks can pass themachine-reading processing steps without any additional overcoat, andcan also be easily overprinted with other inks.

The claims, as originally presented and as they may be amended,encompass variations, alternatives, modifications, improvements,equivalents, and substantial equivalents of the embodiments andteachings disclosed herein, including those that are presentlyunforeseen or unappreciated, and that, for example, may arise fromapplicants/patentees and others. Unless specifically recited in a claim,steps or components of claims should not be implied or imported from thespecification or any other claims as to any particular order, number,position, size, shape, angle, color, or material.

All the patents and applications referred to herein are herebyspecifically, and totally incorporated herein by reference in theirentirety in the instant specification.

What is claimed is:
 1. A non-aqueous magnetic ink comprising: an organicsolvent carrier present in an amount of from about 10 to about 90percent by weight of the ink; an optional dispersant; an optionalsynergist; an optional antioxidant; an optional viscosity controllingagent; an optional colorant; an optional binder; and coated magneticnanoparticles, wherein the coated magnetic nanoparticles are comprisedof a magnetic metal core and a protective coating disposed on themagnetic metal core, the coated magnetic nanoparticles being dispersedin the solvent carrier and further wherein the protective coatingcomprises a mixture of polymeric materials, inorganic oxides, andsurfactants.
 2. The ink of claim 1, wherein the magnetic nanoparticlesare ferromagnetic or superparamagnetic.
 3. The ink according to claim 1,wherein the magnetic metal core is selected from the group consisting ofFe, Mn, Co, Ni, FePt, CoPt, MnAl, MnBi, alloys of the foregoing, rareearth metals and mixtures thereof.
 4. The ink according to claim 1,wherein the polymeric materials are selected from the group consistingof polymethylmethacrylate, polystyrene, polyester, styrene copolymerswith p-chlorostyrene, propylene, vinyltoluene, vinylnaphthalene,methylacrylate, ethylacrylate, butylacrylate, octylacrylate,methylmethacrylate ethylmethacrylate, butylmethacrylate,methyl-α-chloromethacrylate, acrylonitrile copolymer, methyl ether,vinyl ethyl ether, vinyl methyl ketone, butadiene, isoprene,acrylonitrile-indene, maleic acid, and maleic acid ester;polybutylmethacrylate; polyvinyl chloride; polyvinyl acetate;polyethylene; polypropylene; polyvinylbutyral; polyacrylic resin; rosin;modified rosin; terpene resin; phenolic resin; aliphatic or aliphatichydrocarbon resin; aromatic petroleum resin; chlorinated paraffin;paraffin wax, polyvinylidene chloride, ethylene vinyl alcohol,polycaprolactam, polyvinylidene chloride-methyl acrylate copolymer, andcombinations thereof.
 5. The ink according to claim 1, wherein theprotective coating comprises a polymer terminated with a functionalgroup which is selected from a group of amide, amine, carboxylic acid,phosphine oxide, carboxylic ester, alcohol, thiol.
 6. The ink accordingto claim 1, wherein the polymeric materials are selected from the groupconsisting of amorphous, crystalline, homopolymers and copolymers, lowmolecular weight polymers, high molecular weight polymers, and mixturesthereof.
 7. The ink according to claim 1, wherein the inorganic oxidesare selected from the group consisting of silica, titania, zinc oxide,iron oxide, aluminum oxide, and mixtures thereof.
 8. The ink accordingto claim 1, wherein the surfactants are selected from the groupconsisting of anionic, cationic, non-ionic and zwitterionic surfactants,and mixtures thereof.
 9. The ink according to claim 1, wherein the shellcomprises a surfactant selected from the group consisting of oleic acid,cetyl trimethyl ammonium bromide, oleyl amine, trioctyl phosphine oxide,tributyl phosphine, hexyl phosphonic acid, polyvinylpyrrolidone, lauricacid, palmitic acid, stearic acid,poly(1-vinylpyrrolidone)-graft-(1-hexadecene), poly(1-vinylpyrrolidone)-graft-(1-vinylpyrrolidone)-graft-(1-hexadecene),poly(1-vinylpyrrolidone)-graft-(1-triacontene), pentyl beta-hydroxycarboxylic acid, hexyl beta-hydroxy carboxylic acid, cyclohexylbeta-hydroxy carboxylic acid, heptyl beta-hydroxy carboxylic acid, octylbeta-hydroxy carboxylic acid, nonyl beta-hydroxy carboxylic acid, decylbeta-hydroxy carboxylic acid, undecyl beta-hydroxy carboxylic acid,1-butanol, and combinations thereof.
 10. The ink according to claim 1,wherein the solvent carrier is selected from the group consisting oforganic solvent is selected from the group consisting of isoparaffins,methanol, ethanol, n-propanol, n-butanol, benzyl alcohol, methylcellosolve, ethyl cellosolve, acetone, methyl ethyl ketone,cyclohexanone, chlorobenzene, methyl acetate, n-butyl acetate, dioxane,tetrahydrofuran, methylene chloride and chloroform, and mixturesthereof.
 11. The ink according to claim 1, wherein the dispersant isselected from the group consisting of oleic acid, oleyl amine, trioctylphosphine oxide, hexyl phosphonic acid, beta-hydroxy carboxylic acidsand their esters, sorbitol esters with long chain aliphatic carboxylicacids, polyvinylpyrrolidone and derivatives thereof, block copolymerdispersants comprising pigment-philic block and solvent-philic block,and mixtures thereof.
 12. The ink according to claim 1, wherein theviscosity controlling agent is selected from the group consisting ofaliphatic ketones, polystyrene, polymethylmethacrylate, and mixturesthereof.
 13. The ink according to claim , wherein the protective coatinghas a thickness of from about 0.2 nm to about 100 nm.
 14. The inkaccording to claim 1, wherein the magnetic metal core has a shapeselected from the group consisting of needle-shaped, granular, globularcube, hexagonal, oval, spherical and amorphous.
 15. The ink according toclaim 1 having a viscosity of less than 15 centipoise (cP) at atemperature ranging from about 25° C. to about 140° C.
 16. A non-aqueousmagnetic ink comprising: a solvent carrier present in an amount of fromabout 10 to about 90 percent by weight of the ink; an optionaldispersant; an optional synergist; an optional antioxidant; an optionalviscosity controlling agent; an optional colorant; an optional binder;and coated magnetic nanoparticles comprising a magnetic metal core and aprotective coating disposed on the magnetic metal core, the coatedmagnetic nanoparticles being dispersed in the solvent carrier andwherein the protective coating comprises a protective materialcomprising a mixture of polymeric materials, inorganic oxides, andsurfactants and further wherein the protective coating has a thicknessof from about 0.2 nm to about 100 nm.
 17. The ink according to claim 16,wherein the polymeric materials are selected from the group consistingof amorphous, crystalline, homopolymers and copolymers, low molecularweight polymers, high molecular weight polymers, and mixtures thereof,the inorganic oxides are selected from the group consisting of silica,titania, zinc oxide, iron oxide, aluminum oxide, and mixtures thereof,and the surfactants are selected from the group consisting of anionic,cationic, non-ionic and zwitterionic surfactants, and mixtures thereof.18. A non-aqueous magnetic ink comprising: a solvent carrier present inan amount of from about 10 to about 90 percent by weight of the ink; anoptional dispersant; an optional synergist; an optional antioxidant; anoptional viscosity controlling agent; an optional colorant; an optionalbinder; and coated magnetic nanoparticles comprising a magnetic metalcore and a protective coating disposed on the magnetic metal core, thecoated magnetic nanoparticles being dispersed in the solvent carrier andthe protective coating comprises a mixture of polymeric materials,inorganic oxides, and surfactants, and further wherein the ink is usedfor Magnetic Ink Character Recognition (MICR) applications.
 19. The inkof claim 18, wherein the Magnetic Ink Character Recognition applicationcomprises inkjet printing to produce magnetic ink characters or images.